Joining multiple objects removing internal geometry
Place the objects together where they will connect

Duplicate the outside object and place it on a different layer for later.

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Join both meshes



Go into edit mode, select the outer mesh as shown above, and hit ctrl-F.  From the drop-down, choose "Intersect (Boolean)." Now the mesh which would be inside the joined mesh is deleted.



Now bring the other object which you moved to a different layer back, and join it to the other object using the Boolean Modifier, as shown above.

Hope that is the answer you needed!